The overall goal of the proposal is to gain better understanding of the control mechanisms of lung development and growth. Evidence is accumulating that certain growth factors play important roles in normal organ development and tissue repair in response to injury. Hepatocyte growth factor (HGF), a newly identified and characterized growth factor, and its receptor (protooncogene MET protein) are highly expressed in the lung. However, physiological role(s) of HGF in the lung is currently unknown. There is also evidence that human lung fibroblasts in vitro produce HGF. Preliminary data from this laboratory indicate that c-MET is highly expressed in alveolar epithelial type II cells, the cells which synthesize and secrete pulmonary surfactant. Based on these facts, we hypothesize that HGF is produced in the lung by mesenchymal cells and mediates the development of the airway and alveolar epithelium, including surfactant production through paracrine fashion. In this proposal we will scrutinize the hypothesis and will attempt to define physiological and pathological roles of HGF in the lung. The Specific Aims of the proposal are: 1. To characterize the distribution and ontogeny of HGF and HGF receptor (HGF-R) encoded by C-MET in the lungs of control and glucocorticoid-treated rats by in situ hybridization and Northern blot analysis (mRNA), and immunocytochemistry and immunoassay (protein). 2. To study the effects of recombinant HGF on fetal and postnatal lung development by morphological analysis, analysis of surfactant phospholipids, expression of genes encoding surfactant-associated protein A and the Clara cell 10 kD protein (CC10). 3. To study the effects of recombinant HGF on the differentiation and proliferation of rat fetal and postnatal lung epithelial cells in primary cultures, and to monitor cell morphology, cell-specific protein expression, and HGF-induced receptor tyrosine phosphorylation. 4. To investigate the role of HGF in repair of injury to alveolar epithelium in the experimental model of lung injury in rats (silicosis), leading to type II alveolar cell hypertrophy and proliferation. Preliminary data from this laboratory show an increased expression of c-MET mRNA in the lungs of silica-treated rats. Rats of different gestational and postnatal ages, isolated lung cells (type II, Clara, basal), fetal lung explants, and rats with silica-induced lung injury will be used. The results of these studies win clearly establish the functional significance of HGF during lung development and injury.